It depends mostly on where you’re at and where you’re going.
First of all, you have to remove the concept of pain and discomfort from your mind. There is a goal that you’re going to attain and you can’t let the minor things stand in your way.
I trained for many years, from high school & college wrestling to competitive racquetball then on to cycling, marathoning and mountaineering. It doesn’t come easy, but on the other hand, there is nothing that I would rather have been doing.
For an account of how it went for me refer to the book, “Exploits of a Common Adventurer,” by kent irwin.
ps Don’t think that this section of my book will compare to those hundreds of books out there about training. My book is only about me and how I addressed the subject. Keep in mind that I am only a “common” adventurer, not one of those X-games guys!